Dehalogenation Potential of Municipal Waste Incineration Fly Ash

BACKGROUND, AIMS AND SCOPE: In the first part of this paper the main principles which control the dehalogenation of polychlorinated aromatic compounds on municipal waste incineration fly ash (MWI-FA) have been discussed and the model fly ash of similar dehalogenation activity has been proposed. Even if both systems show comparable dehalogenation properties, the main question concerning the postulated identical reaction mechanism in both cases is left unanswered. The other very important point is to what extent is this dechlorination mechanism thermodynamically controlled. The same problem is often discussed in the literature also for the de novo synthetic reactions. From the data it is clear that metallic copper plays a decisive role in the mechanism of the dehalogenation reaction. Although the results reported in the first part strongly support the idea that copper acts in this dechlorination as the reaction component, in contrast to its generally accepted catalytic behaviour, we believed that additional support for this conclusion can be obtained with the help of a thermodynamic interpretation of the mechanism of the reaction. RESULTS AND DISCUSSION: The pathways of hexachlorobenzene dechlorination on MWI-FA and model fly ash were studied in a closed system at 260-300 degrees C under nitrogen atmosphere. These pathways were the same for both systems, with the following prevailing sequences: hexachlorobenzene --> pentachlorobenzene --> 1,2,3,5-tetrachlorobenzene --> 1,3,5-trichlorobenzene --> 1,3-dichlorobenzene. Thermodynamic calculations were carried out by using the method of minimization total Gibbs energy of the whole system. In the calculations, the following reaction components were taken into account: all gaseous chlorinated benzenes, benzene, hydrogen chloride, a gaseous trimer Cu3Cl3, and also Cu2O and CuCl2 as solid components. The effect of the reaction temperature and the amount of copper and water vapour were considered as well. The effect of reaction temperature was determined from the data calculated for the 500 to 750 K temperature region. The effect of the initial composition was determined for the molar amounts of copper = 0.01-3 moles and water vapour = 0.2 to 3 moles per mole of chlorobenzene isomer CONCLUSIONS: The results of hexachlorobenzene dechlorination by MWI-FA and model fly ash under comparable reaction conditions allow us to conclude that both dechlorinations proceed via the same dechlorination pathways, which can be taken as an evidence of the identical dehalogenation mechanism for both systems. The relative percentual distribution of the dehalogenated products depends on the temperature, but not on the initial amount of water vapour or copper metal. On the other hand, the initial amount of copper substantially affects the conversion of the dehalogenation as well as the molar ratio of Cu3Cl3 to HCl in the equilibrium mixture. Comparison of the experimental with thermodynamic results supports the idea that dehalogenation reactions are thermodynamically controlled. RECOMMENDATIONS AND OUTLOOK: Thermodynamic analysis of the dehalogenation reactions may prove useful for a wide range of pollutants. The calculations concerning polychlorinated biphenyls and phenols are under study.     

Effect of reaction time on PCDD and PCDF formation by de novo synthetic reactions under oxygen deficient and rich atmosphere

The effect of reaction time on formation of polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF) was studied under laboratory conditions in the system containing municipal waste incineration fly ash, activated carbon and copper chloride dihydrate at 300 degrees C in 99.999% N2 and N2 + 10% O2 atmosphere. The concentrations of tetra- to octa-chlorinated isomers as well as I-TEQ concentrations of toxic congeners are reported. The mechanism of PCDD and PCDF formation from chlorophenols and chlorinated biphenyls is discussed in the light of the time changes of PCDD/PCDF ratios.     

Environmentally acceptable effect of hydrogen peroxide on cave "lamp-flora", calcite speleothems and limestones

Mosses, algae, and cyanobacteria (lamp-flora) colonize illuminated areas in show caves. This biota is commonly removed by a sodium hypochlorite solution. Because chlorine and other deleterious compounds are released into a cave environment during lamp-flora cleansing, hydrogen peroxide was tested as an alternative agent. In a multidisciplinary study conducted in the Kateinská Cave (Moravian Karst, Czech Republic), 12 algae- and cyanobacteria taxons and 19 moss taxons were detected. The threshold hydrogen peroxide concentration for the destruction of this lamp-flora was found to be 15 vol.%. Based on laboratory experiments in stirred batch reactors, the dissolution rates of limestones and calcite speleothems in water were determined as 3.77 x 10-3 and 1.81 x 10-3 mol m-2 h-1, respectively. In the 15% peroxide solution, the limestone and speleothem dissolution rates were one order of magnitude higher, 2.00 x 10-2 and 2.21 x 10-2 mol m-2 h-1, respectively. So, the peroxide solution was recognised to attack carbonates somewhat more aggressively than karst water. In order to prevent the potential corrosion of limestone and speleothems, the reaching of preliminary peroxide saturation with respect to calcite is recommended, for example, by adding of few limestone fragments into the solution at least 10 h prior to its application.     

Conversion of grazing land into Grevillea robusta plantation and exclosure: impacts on soil nutrients and soil organic carbon

Different studies have shown that the effect of land use conversion on soil nutrients and soil organic carbon (SOC) is variable, which indicates that more investigations that focus on different specific geographical locations and land use types are required. The objectives of this study were (1) to evaluate the effect of grazing land (GL) conversion into Grevillea robusta plantation and exclosure (EX) on soil nutrients and soil organic carbon (SOC) and (2) to examine the impact of soil organic matter (SOM) on soil nutrients. To achieve these objectives, soil samples were taken from a soil depth of 20 cm (n?=?4) in each of the studied land areas. Each soil sample was analysed in a soil laboratory following a standard procedure. Analysis of variance (ANOVA) and Pearson’s correlation coefficient were used for the data analysis. The result indicated that conversion of GL into EX improved the soil electrical conductivity (EC), exchangeable K, cation exchange capacity (CEC), total N and available P (p?<?0.05), while the exchangeable Mg, SOC, available K and SOM were decreased (p?<?0.05). Conversion of GL into G. robusta improved the soil EC, exchangeable (K, Ca, Mg), CEC, SOC, total N, available K and SOM (p?<?0.05). There was a significant relationship between SOM and available P, total N, SOC and EC. There were no significant relationships between SOM and pH, available K and CEC. Finally, the results indicate that both land uses, established in acidic Nitosols, have variable impacts on soil chemical properties and that G. robusta plantation improved most of the soil nutrients and SOC much better than the EX land use.     

Dechlorination ability of municipal waste incineration fly ash for polychlorinated phenols

Pathways of pentachlorophenol dechlorination have been investigated on municipal waste incineration fly ash at 200 degrees C under nitrogen atmosphere. Thermodynamic calculations have been carried out for these dechlorination conditions using the method of total Gibbs energy minimization for the whole system consisting of gaseous components, i.e., chlorinated phenols, phenol, hydrogen chloride and the Cu3Cl3 trimer and of solid Cu2O and CuCl2 components. The effects of water, temperature and of the amounts of the reaction components on the thermodynamic equilibrium have been discussed and the experimental results compared with the calculated thermodynamic data.     

Negative effects of vertebrate herbivores on invertebrates in a coastal dune community

Although competition has been a major focus in ecology for the past century, most empirical and theoretical studies in this area have emphasized interactions between closely related species. However, there is growing evidence that negative interactions among distantly related taxa also occur and may be far more important than previously thought. In this study, we took advantage of an 11-year-old replicated vertebrate-exclosure experiment in a coastal dune community in northern California, USA, to examine the effects of the two most common vertebrate herbivores (jackrabbits and black-tailed deer) on the abundance of the three most visible invertebrate herbivores (two snail, a moth, and a grasshopper species). Our results indicate that four of the six possible pairwise interactions were significantly negative for the invertebrates. Jackrabbits reduced the abundances of snails by 44-75%, tiger moth caterpillars by 36%, and grasshoppers by 62%. Deer reduced the abundances of snails by 32%, increased the abundances of caterpillars by 31%, and had no measurable effect on grasshopper abundance. Our data also revealed that jackrabbits significantly decreased the volume of forbs and common shrubs and the flowering by grasses in our study plots. We were unable to detect an effect of deer on these measures of vegetation. These results suggest that by changing vegetation, jackrabbits may reduce invertebrate populations that are limited by food, protective structures, or microclimate provided by plants. Of these three mechanisms, only shade was strongly supported as limiting snail numbers in smaller-scale manipulations. In most systems, as in this one, the number of pairs of distantly related herbivores far exceeds the number of pairs of congeners. Since interactions among distantly related herbivores may be common in many cases, these interactions are likely to be important and should receive far more attention from ecologists.     

Matrix effects on the de novo synthesis of polychlorinated dibenzo-p-dioxins, dibenzofurans, biphenyls and benzenes

The formation of polychlorinated dibenzo-p-dioxins, dibenzofurans, biphenyls and benzenes in de novo synthesis experiments have been studied on model fly ashes with a wide range of matrices. The model fly ash consisted of 18 selected matrices with the addition of CuCl(2) x 2H(2)O, activated charcoal and NaCl. The studied matrices were not restricted to the commonly investigated matrices with defined chemical composition (silica gel, alumina, florisil) and industrially produced adsorbents with silicate structures (diatomaceous earths), but also included natural occurring matrices (clays, kaolin, bentonite and feldspars). In addition fly ashes from a hazardous waste incinerator were included in the study for comparison. Differences in the isomer composition (homologue profiles and isomer patterns) of the substances formed by de novo synthesis experiments are discussed in dependence on the chemical composition of the studied matrices. The de novo synthesis experiments on matrices with silicate structures resulted in high concentration of mainly perchlorinated aromatic compounds while for other matrices in particular alkaline matrices a homologue shift to lower chlorinated homologues and lower formation rates were found. The paper discusses the resulting PCDD/PCDF pattern and compares them to the PCDD/PCDF profile found in naturally occurring kaolin and ball clay (illite).     

Dehalogenation potential of municipal waste incineration fly ash

BACKGROUND, AIMS AND SCOPE: It is well known that the fly ash from filters of municipal waste incinerators (MWI-FA) shows dehalogenation properties after heating it to 240-450 degrees C. However, this property is not general, and fly ash samples do not possess dehalogenation ability at all in many cases. Fly ash has a very variable composition, and the state of the fly ash matter therefore plays the decisive role. In the present paper, the function of important components responsible for the dehalogenation activity of MWI-FA is analysed and compared with the model fly ash. METHODS: With the aim of accounting for the dehalogenation activity of MWI-FA, the following studies of hexachlorobenzene (HCB) dechlorination were performed: The role of copper in dehalogenation experiments was evaluated for five types of metallic copper. The gasification of carbon in MWI-FA was studied in the 250-350 degrees C temperature range. Five different kinds of carbon were used, combined with conventional Cu(o) and activated nanosize copper powder. The dechlorination experiments were also carried out with Cu(II) compounds such as CuO, Cu(OH)2, CuCl2 and CuSO4. The results were discussed from the standpoint of thermodynamics of potential reactions. Based on these results, the model of fly ash was proposed, containing silica gel, metallic copper and carbon. The dechlorination ability of MWI-FA and the model fly ash are compared under oxygen-deficient atmosphere. CONCLUSIONS: The results show that, under given experimental conditions, copper acts in the dechlorination as a stoichiometric agent rather than as a catalyst. The increased surface activity of copper enhances its dechlorination activity. It was found further that the presence of copper leads to a decrease in the temperature of carbon gasification. The cyclic valence change from Cu(o) to Cu+ or Cu2+ is a prerequisite for the dehalogenation to take place. RECOMMENDATION AND OUTLOOK: Thermodynamic analysis of the dechlorination effect, as well as the comparison of dechlorination pathways on MWI-FA and model fly ash, can provide a deeper understanding of the studied reaction.     

Leaf drop in evergreen Ceanothus velutinus as a means of reducing herbivory

Conventional explanations for deciduousness do not include losses to herbivory. However, a recent explanation posits that deciduous leaf drop allows trees to reduce their herbivore loads and that this benefit of the deciduous habit may partly offset lost opportunities for photosynthesis. Much of the damage caused by chewing herbivores occurs early in the season when adult insects colonize as new leaves are expanding; trees without leaves from previous leaf flushes at this time are less attractive and suffer less cost of herbivory. I tested this hypothesis using Ceanothus velutinus, an evergreen shrub that shows considerable individual variation in leaf retention. Stems that held more leaves through winter experienced more chewing damage the following season. Stems with leaves experimentally removed through winter also were less likely to receive chewing damage the following season. At least some herbivores in this system make oviposition decisions before new leaves have expanded, and old leaves may provide cues about the suitability of the stem. Holding leaves through winter increased the likelihood of herbivory, and experimental protection from herbivores caused 60% greater inflorescence production compared to unprotected stems. However, the cost of leaf retention was more than offset by an overall benefit. Stems that were allowed to keep winter leaves produced larger new leaves in summer and expanded them more rapidly in the season than stems with winter leaves experimentally removed. As a result, stems with leaves through winter experienced higher survival, four times as many inflorescences, and 40 times as many fruits as shoots that were experimentally defoliated. Losses to herbivores may be an unappreciated cost of leaf retention, and cost-benefit models of deciduous and evergreen behavior should include these losses.     

Damage-induced resistance in sagebrush: volatiles are key to intra- and interplant communication

Airborne communication between individuals, called "eavesdropping" in this paper, can cause plants to become more resistant to herbivores when a neighbor has been experimentally clipped. The ecological relevance of this result has been in question, since individuals may be too far apart for this interaction to affect many plants in natural populations. We investigated induced resistance to herbivory in sagebrush, Artemisia tridentata, caused by experimental clipping of the focal plant and its neighbors. We found no evidence for systemic induced resistance when one branch was clipped and another branch on the same plant was assayed for naturally occurring damage. In this experiment, air contact and plant age were not controlled. Previous work indicated that sagebrush received less damage when a neighboring upwind plant within 15 cm had been experimentally clipped. Here we found that pairs of sagebrush plants that were up to 60 cm apart were influenced by experimental clipping of a neighbor. Furthermore, we observed that most individuals had conspecific neighbors that were much closer than 60 cm. Air contact was essential for communication; treatments that reduced airflow between neighboring individuals, either because of wind direction or bagging, prevented induced resistance. Airflow was also necessary for systemic induced resistance among branches within an individual. Reports from the literature indicated that sagebrush is highly sectorial, as are many desert shrubs. Branches within a sagebrush plant do not freely exchange material via vascular connections and apparently cannot rely on an internal signaling pathway for coordinating induction of resistance to herbivores. Instead, they may use external, volatile cues. This hypothesis provides a proximal explanation for why sagebrush does not demonstrate systemic induced resistance without directed airflow, and why airborne communication between branches induces resistance.